Before starting, make it clear that it is a study, it does not imply a generality, but it is a statistical data.
The research, conducted by Finnish and British scientists, concluded that women who had a male twin brother were less likely to marry (15% less) and have children (25% less), and to have them, gave birth an average of two children less than those who had a twin sister.
The explanation seems to lie in the influence on the brother's testosterone hormone to which the girl is exposed for nine months inside the uterus.
The same does not happen in the case of children, as both the fetus of the boy and the girl are exposed to similar levels of estrogen, the female hormone.
That is why girls are more susceptible to being affected by the testosterone levels of the male, which would affect their ability to have children in the future.
For their part, experts also pointed out that these girls, women married less, perhaps because of their somewhat manly features that made them less attractive.
It is very important that we know that research has been based on data from births and weddings of the eighteenth and nineteenth centuries to obtain genuine results, without being affected by current advances in medical care and contraception.
